Today, LED lighting is gaining wide-spread acceptance in automotive, industrial and other lighting applications. As is commonly known and appreciated, LED lighting generally requires less energy to produce a desired quantity of light, where the quantity of light is often expressed in lumens and along a correlated color temperature range, often expressed in degrees Kelvin. In some LED applications, such as automobile front head-light applications, relatively high LED string voltages, often ranging between 4 to 50 Volts, and high currents, often ranging from 100 mAmps to 3 Amps are commonly used. Such LED systems are commonly used to produce a range of Lumens over a given range at a color temperature in degrees Kelvin that is not noticeably perceptible by a driver. The quantity and temperature range of light produced, however, may vary based upon operating, user preference and other considerations. It is to be appreciated that the light produced by LED units is commonly proportional to the current used to drive the LED units. Given these voltage, current, lumen and temperature ranges, the regulation of the current flowing through the LEDs is very important.
As shown in FIG. 1, one common circuit 100 used today to regulate the current flowing through high power LED units utilize circuits that include a similar power source 102, connected to a DC/DC buck convener module 104. The buck converter module 104 commonly includes coils and capacitors which facilitate the storage and discharge of electrical energy, these inherent capabilities buck converters are referred to herein as providing an enemy storage module. Often the buck converter module 104 and related switching components are provided in a common ballast 106, but, may be provided separately or as components of larger systems or units. The principles of operation and elements of such buck converter module 104 are well known in the art and are not described herein but are incorporated herein by reference and by inherency. It is to be appreciated that one or more of the components of the buck converter module 104 shown in FIG. 1 may be replaced and/or augmented by other known circuit components and configurations. For example, diode 126 could be replaced by a N-type field effect transistor (FET) for a synchronous converter.
Further, it is to be appreciated that the electrical characteristics of one or more of the components of a buck converter module 104, as shown for example in FIG. 1, are illustrative only and can be considered to be elements of other components of the embodiments shown. As is commonly known, the output power, as commonly expressed in terms of an LED current ILED and an LED voltage VLED, of the buck converter-module 104 provides electrical power to one or more LED units 108a,b,c-108n. The LED units 108a,b,c-108n may be driven individually, collectively or some combination in-between by a pixel driver module 110 or a similar module (if any). The pixel driver module 110 may be used to control whether any given LED unit 108a-n is powered or short-circuited, at any given time, by selectively opening/closing irrespectively one or more pixel driver switches 112. Often the pixel driver module 110 adjusts the opening/closing of the one or more pixel driver switches 112 in accordance with then desired lighting conditions, as may be sensed, selected, or determined based upon ambient light sensors, speed, user preferences, in accordance with regulations and other considerations.
Often a first switch 116, such as an N-channel P-channel MOSFET transistor, is used to control the operating state, “on” or “off”, of the buck converter module 104. The peak current IMAX of the current fun generated through the buck converter module 104 through switch 116, and thereby to the LED units 108a-n, may be sensed at the output of the buck converter module 104 using a current sensing element 117, for example, a resistive element 118 and an operational amplifier 120. If the optional filtering capacitor CI 174 is omitted, it is to be appreciated that the LED current ILED is the same as the coil current I1. In other embodiments, other forms of current sensing devices and/or modules are often utilized. The voltage across the resistive element 118, as sensed by the operational amplifier, reflects the peak current IMAX provided to the LED units 108a-n at any given time. By controlling the respective “on” and “off” periods of the first switch 116, the currents ILED provided to the LED units 108a-n may be regulated. It is to be appreciated that when current sensing element 117 is placed series with LED units 108a-n, the real current flowing through the LED units 108a-n is sensed. In other embodiments, the current may be sensed at the first switch or otherwise. For such other embodiments, it is to be appreciated that the current sensed is not the real current provided to the LED units 108a-n due to the filtering effects of the capacitor CI 124. Capacitor CI 124 is often positioned on the LED side of coil 122 such that the current sensing element 117 is able to sense the instantaneous coil current. It is to be appreciated that current sensing element 117 is not an element of the buck converter module 104.
As shown, buck converter module 104 commonly includes a coil 122 having an inductance L. In high current LED applications and in view of economic, design and other considerations, it is often desirable to reduce the inductance L of the coil 122 and eliminate the need for any external sensing elements such as resistive elements 118 which commonly drain too much power, are expensive, utilize too much physical space on electrical circuit boards and in view of other constraints.
Ideally, a low cost, low inductance system is needed which enables one to regulate the average currents provided to the LED units by the buck converter module 104. These competing desires of low cost, low inductance coils, exclusion of external sensing elements and others, while maintaining a desired average current and power provided to the LED units, with varying voltage demands of such LED units often are further constrained in that a reduction of the coil 122 inductance L of requires an increase in the frequency at which the fast switch 116 is switched “on” and “off.” It is to be appreciated that as the inductance L of coil 122 decreases, the switching frequency of the first switch 116 must increase in order to maintain a desired average current and acceptable ripple current provided to the LED units 108a-n. 
Further constraining the above considerations and concerns is the need to avoid the generation of undesired electro-magnetic emissions during operation. It is commonly known that buck converters generate Electro-Magnetic Radiation (EMRs). High EMRs can influence the operations of other circuits and components in automobile and other implementations of high power LED units. Accordingly, the Electro-Magnetic Compatibility (EMC) of LED driver units is often highly regulated, especially in motor vehicles. Commonly, EMC concerns limit the permissible frequency range of buck converter modules to frequencies below 500 kHz or above 1.8 MHz and below 5.9 MHz. As such, today a need exists to regulate not only the average current but also the switching frequency of LED driver units.
As shown in FIGS. 2A and 2B, today's known circuits (such as the exemplary circuit shown in FIG. 1) commonly attempt to regulate high power LED modules by generating a ripple current R, where the ripple ΔR of the coil current, I1, is controlled, over time, by the switching of the first switch 116 “on” and “off.” These periods are shown in FIG. 2 by ton and toff.
In FIGS. 2A and 2B, the “on” period for the first switch 116 is shown by ton. The “off” period for the first switch 116 is shown by toff, which is proportional to the voltage over the coil (VLED-VLC). That is, for these module designs, it is commonly appreciated that the time off period toff depends on the coil voltage during the “off” time, and is close to the voltage VLED of the LED units 108a-n, with the often negligible and disregarded differences arising from the forward voltage provided by the diode 126 during the “off” time. That is, as VLED increases, toff needs to decrease to maintain a constant current ripple ΔR, and vice versa. This relationship can be expressed mathematically, where L is the value of the coil 122 of the buck converter 104, as follows:(toff×VLED)/L=ΔR. 
It is to be appreciated that, per these prior art approaches, the switching frequency is not controlled, and is varying in response to variations in the input voltages VIN to the buck converter module 104, the properties of the coil 122, and the voltage needs VLED of the LED units 108a-n, where VLED may vary over time based upon the variations in the number of LED units on and off at any given time and the power needs of such LED units.
Further, it is to be appreciated that such designs require the inductance L of the coil 122 to be known and/or the system to be calibrated (and re-calibrated) to such inductance. The inductance of a coil may vary over time and in response to operating conditions. Variations in the inductance L may cause undesirable errors to arise in the output current ILED.
Therefore, an apparatus, system, and method (collectively, “systems”) is needed for a controlling the average current of a high-powered DCDC LED driver module. Such systems facilitate the use of low inductance coils, and buck converter modules which can operate, for a particular implementation, independent of a coil inductance, input voltage, and varying load conditions while maintaining the average current of the buck converter module. Further, systems are needed where current sensing occurs during the “on” time of the first switch and thereby limits power losses while improving system efficiency. Further, systems are needed which support asynchronous and synchronous operating modes, where, for example, asynchronous operations may occur when diode 126 is used with synchronous operations occurring when a MOSFET or similar transistor, instead of diode 126, is utilized.